Systems with fast self-learning ability, high precision, and effective vibration attenuation play key roles in many areas including advanced manufacturing, data-storage systems, micro-electronic systems, and medical robotics. This dissertation focuses on three topics to achieve greater autonomy and accuracy in high-precision systems: (1) iterative learning control (ILC), (2) vibration estimation and (3) vibration control.
ILC is an effective technique that improves the tracking performance of systems that operate repetitively by updating the feedforward control signal iteratively from one trail to the next. The key in the design of ILC is the selection of learning filters with guaranteed convergence and robustness, which usually involves lots of tuning effort especially in high-order ILC. To facilitate this procedure, this dissertation presents a systematic approach to design learning filters for arbitrary-order ILC with guaranteed convergence, robustness and ease of tuning. The filter design problem is transformed into an H-infinity optimal control problem for a constructed feedback system. The proposed algorithm is further advanced to the one that explicitly considers system variations based on $\mu$ synthesis. High-order ILC enables the system to improve the performance through learning from more memory data with higher efficiency and guaranteed robustness. The proposed ILC design method is applied to a laboratory testbed of the Nikon wafer scanning system, and holds the potential for other applications such as intelligent manufacturing and rehabilitation systems that need considerable iterations of learning.
High-precision systems are usually subjected to high-frequency vibrations. Vibration estimation and suppression play key roles in high-precision systems. This dissertation explores two techniques of vibration estimation: disturbance observer (DOB) and extended state observer (ESO). A generalized DOB design procedure is proposed for a multi-input-multi-output (MIMO) system based on H-infinity synthesis. The proposed technique releases the DOB design from the plant inverse, assures the stability and minimizes the weighted H-infinity norm of the dynamics from the disturbance to its estimation error. A phase compensator is proposed for the ESO to push its estimation bandwidth from low frequency to high frequency; the ESO's bandwidth is further pushed beyond the Nyquist frequency by including the nominal model of the disturbance dynamics.
Based on the frequency-domain characteristics of the vibrations which can be obtained either from vibration sensors or vibration estimators, this dissertation presents a systematic frequency-domain design methodology for sliding mode control (SMC) to effectively suppress vibrations as well as keep excellent transient performance. Specifically, a frequency-shaped sliding mode control is proposed by introducing the loop-shaping technique into the design of the sliding surface. The sliding surface is optimized based on H-infinity synthesis with guaranteed stability and desired frequency characteristics. This work extends SMC's applications to high-precision control systems which have demanding requirements in both time and frequency domains, and hold the potential to break some limitations of linear controls. The proposed vibration estimation and suppression techniques are applied to high-precision high-speed data storage systems, and significantly enhance vibration attenuation while maintaining excellent transient performance.
